1. Field of the Invention
This invention relates generally to apparatus and processes for water impurity analysis and to impurity analysis of various other liquids as well. More particularly, the present invention concerns apparatus and processes for physical characterization of liquid drops as the liquid builds up and then drops from a sample needle or other source. Even more particularly the present invention is directed to liquid drop characterization through utilization of infrared liquid drop measuring and computer modeling to measure a liquid drop as it builds up and then to measure the falling liquid drop.
2. Description of the Prior Art
In many industrial and laboratory situations an authoritative test is needed for determining the degree of pollution that exists in a liquid, particularly water, stream. Water pollution due to the presence of organic materials has been measured indirectly in BOD analysis by how actively bacteria will use up the organic material in a given sample and consume oxygen from the sample. Since BOD analysis is an exceedingly slow procedure, it has been determined to be more appropriate to measure liquid samples directly for contamination due to the presence and volume of organic materials and to provide a system for rapid and low cost sample analysis. A low cost and rapid analysis process known as Total organic carbon (TOC) analysis has proven quite acceptable for this purpose. Moreover, TOC data can be readily converted to BOD or COD data if desired.
TOC analysis is typically conducted by injecting a known volume of water or other liquid into a furnace containing acid coated quartz chips and being at a sufficient temperature, 150.degree. C., for example, to convert the inorganic carbon in the sample to CO.sub.2 which is then measured by an infrared analyzer that is sensitive to CO.sub.2. Another like volume from the same sample is then injected into a high temperature furnace, 950.degree. C. for example, containing a catalyst to aid complete combustion. Oxygen is then metered into a reaction tube causing the total carbon, inorganic and organic, to be converted into CO.sub.2. The volume of the CO.sub.2 of the sample is then measured by an infrared analyzer. The CO.sub.2 generated by complete combustion is directly proportional to the total carbon in the sample stream. A problem with TOC analysis of this nature is that inaccuracies can result from the coordination of two separate measurements, especially if the ratio of of inorganic carbon of the sample as compared to total carbon is large. The use of a catalyst can also create some problems from the standpoint of accuracy.
More recently, TOC analyzer manufacturers have introduced analyzers using a low-temperature ultra-violet (UV) promoted chemical oxidation method which offers certain advantages over combustion TOC analysis. These systems measure TOC directly be means of an acidification and scrubbing pretreatment system which removes carbonates prior to oxidation. The feasibility of UV/persulfate technique for oxidizing organic carbon was demonstrated a number of years ago and is well documented relative to its excellent oxidation efficiency. The major advantage of a low temperature UV promoted chemical TOC system is that all reactions take place in the liquid phase, resulting in increased reliability and reduced TOC analyzer maintenance requirements.
Total organic carbon (TOC) analysis is often considered beneficial as a rapid screening method to determine requirements of more costly and time-consuming specific toxic and other organic component analyses. In many cases, depending upon the application, TOC analysis is an adequate and inexpensive substitute for more time consuming and more expensive alternative methods for determination of water quality, provided the TOC analyzer being employed has sufficient sensitivity and capability. These more time consuming and expensive water quality determination methods, for example, include among others, the biochemical oxygen demand (BOD) test and the chemical oxygen demand (COD) test.
Although the low temperature UV promoted chemical TOC system has gained wide acceptance in the field of water quality testing, tests of the inventors has shown that TOC analysis of enhanced accuracy will result from physical characterization of liquid drops in connection with UV promoted chemical TOC analysis.
Thus, it is a feature of the present invention to provide methods and apparatus for accomplishing physical characterization of sample liquid drops as they build up relative to a known drop support structure;
It is another important feature of the present invention to provide for liquid drop characterization through utilization of infrared liquid drop measuring and computer modeling to measure a liquid drop as it builds up and then to measure the falling liquid drop.
Briefly considered, by optically (infrared light between 3.8 and 4.3 nanometers) measuring a falling drop, and/or by characterizing the manner by which a sample drop is formed, a very precise way of determining the exact volume of a liquid sample is accomplished. Very often, sample volume is directly proportional to concentration levels of the chemical constituent to be measured. By computer modeling a falling drop can be quantified as to volume, rather than depending on the otherwise standard way of injecting a "known" volume (which, through inaccuracies of sampling, may actually vary).
To accomplish sample drop characterization an infrared-emitting light is shone through a quartz window or a window composed of other suitable material and directed onto an infrared detector with an optical filter in the water vapor/liquid band, and measures not only the falling drop, but drop formation as it builds up. The infrared detector provides a signal output representing sample drop measurement, which signal output is input to a computer or microprocessor for processing and display, such as by a computer monitor, liquid crystal display, printer output, etc.
A liquid drop characterization head is provided which is mounted to a slide member, particularly a slide member composed of polytetrafluoroethylene or any other suitable substantially inert material which is movable between a drop characterization position, positions for conducting sample liquid into reactor ovens and a sample drain position. The liquid drop characterization head defines an upper, internally threaded opening that is in communication with the central passage having an infrared transparent tube, typically composed of quartz, sapphire or any other suitable infrared transparent material. A liquid drop supply, typically in the form of a needle is received by the internally threaded opening. The infrared transparent tube is positioned with its upper end within the central opening and with its external surface sealed to the head structure by an O-ring seal that is located within an O-ring groove. An infrared emitter is located within a lateral emitter receptacle of the head while an infrared detector is located within an oppositely located lateral detector receptacle in position to receive filtered infrared radiation which is altered by sample drop characterization and to output electrical signals responsive to drop characterization.